INVESTIGATIONS OF GAS-TO-PARTICLE CONVERSION IN THE ATMOSPHERE

Continental aerosol particle size distributions were measured as a fun ction of time at the background station Aisetas and in the suburb of V ilnius. Marine aerosol particle formation was studied in outdoor photo chemical chamber experiments performed on the coast of the Baltic sea. The functional dependence of the particle diameter growth rate on the particle size was calculated from the aerosol particle size distribut ion data and was compared with the theoretical predictions for the par ticle growth due to vapor condensation or due to the adsorption of aer osol precursor gases on the particle surface or within an airborne dro plet. It was shown that during summer months condensation of low press ure vapors formed by gas phase homogeneous chemical reactions was pred ominant mechanism of the continental aerosol particle growth. While in winter growth of a submicrometer continental aerosol particle was fre quently governed by two competing processes: condensation of low press ure vapors and heterogeneous oxidation of aerosol precursor gases insi de the liquid droplet. Ozone was found to be an active oxidant in the heterogeneous aqueous phase chemical reactions. The outdoor photochemi cal chamber experiments showed that aqueous phase chemical reactions w ere responsible for the formation of marine sulfuric acid aerosol part icles from the dimethylsulfide. After these particles were partially n eutralized by ammonia to the ammonium sulfate or bisulfate, their furt her growth was observed to be surface limited.